The mitral valve is one of the most crucial of the four valves of the human heart, preventing the regurgitation of blood from the left ventricle into the left atrium during contraction of the heart. Located between the left atrium and the left ventricle, the mitral valve includes two leaflets positioned to block blood flow in a closed state while allowing blood flow in an opened state.
The mitral valve is opened and closed by a pressure differential between the left atrium and left ventricle and by a complex network of collagenous cord-like structures called chordae tendineae that extend from the free edges of the mitral valve leaflets to the papillary muscles on the ventricular wall of the heart. As the papillary muscles contract, they pull on the leaflets and thereby open the mitral valve, allowing blood to flow into the left ventricle. As the papillary muscles relax, the pull on the leaflets is reduced, causing the mitral valve to close and thereby block blood flow into the left ventricle.
Normal operation of the mitral valve can be impaired when the valve leaflets fail to coapt or fully close, allowing regurgitated blood to flow back into the left atrium. This mitral valve regurgitation is often caused by a congenital valve defect or by changes to the heart geometry due to disease. For example, an infection may cause the mitral valve annulus to enlarge and thereby change the position and orientation of the valve leaflets. In another example, a mitral valve defect may cause prolapse or a mismatch of the leaflets, allowing blood flow to regurgitate back into the left atrium.
One early approach to treatment of an insufficient mitral valve involved surgical replacement with an artificial valve. In these procedures, open-heart surgery was typically performed on the patient to replace the faulty valve with either a mechanical or biologically derived valve. While this treatment procedure has been improved with time, significant limitations still exist. For example, the removal and replacement of a mitral valve is highly invasive and therefore greatly increases the risk of serious complications such as infection or rejection.
Other surgical techniques have been developed to reduce the amount of heart remodeling necessary with valve replacement. One such technique is known as bowtie repair, in which a center region of each mitral valve leaflet is sutured together. Another technique involves creating a placation around the valve annulus, thereby reducing the cross-sectional area of the valve annulus. While these techniques require less remodeling than valve replacement, a substantial amount of remodeling is still required. Further, it can be difficult to evaluate the efficacy of the surgical procedure before the conclusion of the surgery.
In yet another technique, an annuloplasty ring is sewn within the annulus of the mitral valve. Since the diameter of the annuloplasty ring is smaller than the diameter of the mitral valve annulus, the leaflets of the valve are moved together, increasing coaptation. In addition to also being highly invasive, annuloplasty rings generally distort the natural curved shape of the mitral valve and can further limit the contractility of the annulus.
While the techniques described above have been used with some success for the treatment of mitral valve deficiencies, additional treatment procedures are needed that require little or no remodeling of the heart. Further, additional treatments are needed that can be performed with minimal invasiveness and yet can more effectively reduce or eliminate mitral valve regurgitation.